President Donald Trump speaks with Qatar's Emir Sheikh Tamim Bin Hamad Al-Thani, during a bilateral meeting at a hotel in the Saudi capital Riyadh on May 21, 2017. In a series of morning tweets, President Donald Trump threw Washington's relations with Doha into deep crisis on June 6, 2017, and raised doubts about the future of the largest U.S. air base in the Middle East.

President Donald Trump speaks with Qatar's Emir Sheikh Tamim Bin Hamad Al-Thani, during a bilateral meeting at a hotel in the Saudi capital Riyadh on May 21, 2017. In a series of morning tweets, President Donald Trump threw Washington's relations with Doha into deep crisis on June 6, 2017, and raised doubts about the future of the largest U.S. air base in the Middle East.

Saudi Arabia and several Middle East neighbors have severed diplomatic ties with the tiny nation of Qatar. A donnybrook in a faraway land? Yes. A squabble of little relevance to America? No.

First, the reason for the rift: The Saudis, along with Bahrain, Egypt, Yemen and the United Arab Emirates, accuse the Qatari government of backing Islamist groups in the Middle East, including Islamic State, al-Qaida and the Muslim Brotherhood. Perhaps Saudi Arabia's biggest beef with Qatar: The Sunni-dominated Riyadh government accuses Doha of backing militant groups supported by Shiite-majority Iran, the Saudis' main nemesis in the Middle East.

The latest evidence: Two weeks ago, Qatar's state-run news agency published remarks allegedly made by the country's emir that called Iran "a regional and Islamic power that cannot be ignored." Qatari leaders say the news agency was hacked, and that the published comments were fake; Saudi Arabia and its neighbors dismiss the denial. The Saudis also accuse the Qatari government of looking the other way when its citizens funnel money to Islamist groups, a pot-calling-the-kettle-black charge from Saudi Arabia, which has been accused by the West of the same behavior.

On Monday, the Saudis shut down their border with the Qatari peninsula, which imports much of its food across that border. The Saudis and other countries have also begun withdrawing their diplomatic staffs, and two major air carriers, the UAE-based Etihad and Emirates airlines, shut down service to Doha. So have other regional carriers. The Saudi-led coalition has also closed sea links to the peninsula. Those nations are also evicting all Qatari citizens.

Bad for Qataris, but also bad for the U.S. Why?

Because defeating terrorism — a suicide bomber trying to get into a stadium, a car of knife-brandishing militants plowing into pedestrians on a bridge, a man with an assault rifle spraying gunfire into a packed nightclub — requires that countries put up a united front, share intelligence, destroy militant hubs and financial conduits, and coordinate security strategy.

Qatar also plays a direct, crucial role in the American fight against Islamic State. The U.S. uses its Al Udeid Air Base in Qatar, home to about 10,000 American troops, to launch airstrikes on Islamic State strongholds in Iraq and Syria. Secretary of State Rex Tillerson and Defense Secretary Jim Mattis both said the rift between Qatar and its Gulf neighbors won't affect the air campaign against Islamic State. The U.S. can always relocate its air campaign elsewhere if Qatar becomes unworkable. That said, any disruption in the fight against Islamic State militants would be a setback.

Leaders in Russia, Turkey and Kuwait have been talking about ways to solve the split between Qatar and its neighbors. President Donald Trump has been doing the opposite. On Tuesday, he endorsed Saudi-led actions against Qatar in a tweet that amounted to self-praise for his speech in Saudi Arabia on May 21, which embraced a pro-Saudi view of the Middle East. "So good to see the Saudi Arabia visit with the King and 50 countries already paying off," the president tweeted. "They said they would take a hard line on funding extremism and all reference was pointing to Qatar. Perhaps this will be the beginning of the end to the horror of terrorism!"

Analysts say Saudi leaders and their Gulf allies took Trump's speech in May as a green light to turn the screws on Qatar. "Donald Trump now accepts the view of Saudi Arabia as a strategic bastion in the Arab and Islamic world," Fawaz Gerges, a professor of Middle East studies at the London School of Economics, told The Washington Post. "What you are seeing now is that the Saudi-led coalition feels empowered. They are on the offensive."

Indeed, on the offensive against fellow Arab states, at a time when they need to unify against terrorists capable of the carnage we saw in London over the weekend, in Manchester on May 22, in Nice a year ago. ... The list grows.